ok so i guess i am a little foggy from the summer break. can someoen help me with this question?
if cos t = (4/5), then find cos (t + pi)
I am totally lost, so please help me.
Let's try to see what $\displaystyle \cos (t + \pi)$ simplifies to, in terms of sine and cosine...
$\displaystyle \cos (t + \pi)=\cos t\cos\pi-\sin t\sin\pi$ <-- Sum Identity
Note that $\displaystyle \cos\pi=-1\text{ and }\sin\pi=0$
Thus, our expression simplifies to $\displaystyle \cos(t+\pi)=-\cos t$
I'm sure you can take it from here...
I hope this helps
--Chris
EDIT: JaneBennet beat me...